Aphelidium

Aphelidium species are endoparasites of freshwater green algae. Aphelidium belongs to the phylum Aphelida, and is part of the Opisthosporidia, a sister clade to Fungi.^[3] The cells of Aphelidium are much smaller than the cells of its green algae host, which is protected by a robust cell wall. Aphelidium have evolved a remarkable life cycle to defeat host's defenses.

The infection process for Aphelidium is notable for its method of entry. An Aphelidium cyst attached to a potential host will raise its internal pressure by expanding the posterior vacuole before using the sudden release of this pressure to defeat the host cell wall and jet itself into the host.^[3] As parasites of green algae, Aphelidium have important implications for the production of biofuels using algaculture.^[4]